1. Field of the Invention
This invention relates to analog-to-digital converters (ADCs) and related conversion methods, and more particularly to ADCs that are adaptable to multiple-channel analog inputs.
2. Description of the Related Art
Numerous different ADC architectures are available, such as successive-approximation, flash, dual-ramp and staircase devices. Such converters are described in general in Fink and Christiansen, ed, Electronics Engineer's Handbook, McGraw-Hill, 1989, pages 3.42-3.43, 8.69-8.77, 16.63-16.67.
One of the limitations of presently available ADCs is the difficulty in providing monolithically integrated converters with a multi-channel input capability. Monolithic integration would be very helpful in applications which have stringent noise, power, space and performance requirements. Without such integration, cost considerations can dictate that only a single ADC be used to service multiple channels. In this event, the ADC is multiplexed among the different channels, which typically number 16. This is the approach taken in Talambiras, "Some Considerations in the Design of Wide-Dynamic-Range Audio Digitizing Systems", Proc. Audio Engineering Society 57th Conv., May 10, 1977, pages 164-170, and also in the 1988 Analog Devices Data Book, pages 3.13-3.22 for the AD368/AD369 converters. Both of these references multiplex successive approximation converters. This requires a large amount of power, and it is difficult to monolithically integrate the multiplexer, programmer and analog-to-digital function as indicated in the two references on the same chip.